How Many Types of PCB Vias Are There and How to Choose?

Printed Circuit Board is the foundational element of modern electronics, providing intricate pathways that facilitate the proper functioning of devices. Amidst the various components and features of PCB, one crucial yet often overlooked aspect is the PCB via. Within each PCB, an intricate web of electrical connections exists. Vias serve as small conduits that establish connections between different layers of the PCB. These drilled holes are coated with conductive materials like copper to ensure seamless electrical pathways. They offer features such as power distribution and linking power and ground planes, enhancing heat dissipation and energy flow efficiency. However, the multitude of types of via in PCB can typically leave engineers unsure about the best choice for their specific applications. To address this challenge, FS Technology is here to offer comprehensive solutions and guidance, helping engineers make informed decisions when it comes to selecting the most suitable vias.

What is PCB Via?

A PCB via is a small hole that passes through adjacent layers of a PCB board, aiding in the transfer of signals and power between these layers. In a multilayer PCB, the circuits among different layers are isolated, and vias play a crucial role in establishing connections between these internal layers. In essence, vias act as bridges, facilitating seamless communication between components situated on various layers. Without vias, the intricate interconnections commonly utilized in electronic devices would become challenging to achieve.

Components of Via

Pad: Serving as a connection point for the via, the pad establishes a link between the via and the component or trace on the PCB board’s surface. Pads are typically crafted using conductive materials like copper, ensuring a secure electrical connection.
Hole: The hole acts as a physical conduit, enabling the passage of vias between different layers. It is either drilled or etched into the circuit board’s insulating substrate to facilitate vertical connections across layers.
Annular Ring: Refers to the copper area surrounding the hole on the board’s surface. This ring enhances stability and conductivity by providing larger contact surfaces. The size of the annular ring can impact the reliability and performance of the vias.
Barrel: Constitutes the conductive inner wall of the hole, creating a continuous pathway that links various layers of the PCB board. Signal quality and efficient power distribution depend on the quality of the barrel’s construction.
Solder Mask: Protective layer applied to the PCB board’s surface, leaving openings for pads and vias. It prevents solder bridges and shorts during the PCB assembly process, ensuring separation between the via and surrounding components.
Plating: Involves depositing a thin layer of metal, usually copper, onto the hole’s internal walls and pad surfaces. This process enhances conductivity and establishes a reliable connection between the via and other parts of the circuit.

Features of Via

Signal Routing: A via plays a crucial role in facilitating signal movement across diverse layers of a board. It ensures seamless signal flow amidst intricate and densely packed electronic circuits, facilitating proper interaction among components. Operating as a bridge, a via safeguards interference-free and distortion-free signal traversal. In high-speed digital circuits, preserving signal quality and reducing signal loss is paramount.
Power Routing: Stable functionality of electronic devices hinges on effective power distribution. A via aids in establishing dedicated channels for grounding and power connections, ensuring uniform electrical energy supply to various components. By providing a low-resistance connection between different power planes, a via helps address issues like voltage fluctuations, noise, and overheating.
Trace Density: Modern electronics demand compact designs with elevated component density. A via empowers engineers to route traces across multiple layers of a board, thereby increasing trace density. This capability allows for the creation of intricate, space-efficient structures, effectively utilizing available space. Consequently, compact electrical devices can be realized without compromising utility or performance.
Signal Transmission: A via’s ability to establish connections between distinct layers significantly influences reliable signal transmissions. It mitigates signal propagation delays, establishes shorter and more direct signal pathways, and expedites overall system performance. Furthermore, a via contributes to minimizing crosstalk, signal isolation, and interference among neighboring traces or components. Precision in impedance control and a well-designed via curb signal reflections and sustain signal quality.

How Many Types of Vias Exist in PCB

Through Hole Via

Through-hole via serves a pivotal role in PCB employed within electronic devices, facilitating electrical connections across distinct board layers. This type of via traverses the entire thickness of the PCB, affording a conduit for seamless signal and power transmission. This via is introduced during the PCB manufacturing process, involving drilling through the board and subsequent plating of the hole walls with conductive materials to establish electrical links. This meticulous procedure ensures dependable and precise connections amidst diverse board layers. As shown in the figure above, PTH stands for plated through hole, which is used to insert components in through-hole PCB assembly, and NPTH stands for non-plated through hole, which plays a fixed role instead of electrical connection.

Through-hole via furnishes an array of advantages, including robust mechanical stability and the capability to manage high currents. It excels in securing connections and accommodating components requiring resilient mounting, such as larger DIP components like transformers and capacitors, as well as applications demanding robust mechanical endurance.

However, the through-hole via is not without limitations. It consumes additional space on the board, potentially constraining the available routing area for components and traces, a factor to weigh in designs that aim for miniaturization or dense packing. Additionally, the presence of this via can impact signal quality by introducing impedance mismatches and signal reflections.

Microvias

Microvias, characterized by their diminutive size, play a specialized role in modern printed circuit boards by establishing connections among different layers. With diameters ranging from 0.05 mm to 0.15 mm, these small wonders are pivotal in densely populated electronic projects, ensuring effective signal transmission and power distribution.

Manufactured through techniques like laser drilling or sequential build-up, micro vias offer a host of advantages. They minimize signal propagation delays, enhance routing density, and facilitate efficient thermal management. These attributes find application in high-performance electronic devices such as mobile phones, laptops, and networking tools. The advent of micro vias has spurred a revolution in PCB design, enabling compact and intricate layouts that contribute to the overall miniaturization and functionality of electronic devices.

However, their diminutive nature presents challenges in terms of manufacturing reliability and accuracy. Overcoming these hurdles necessitates meticulous engineering and stringent quality control measures during the manufacturing process.

Buried Via

Buried via board design facilitates the efficient routing of intricate circuits and compact layouts. This via represents a unique connectivity structure that establishes internal conductive connections across multiple PCB layers while remaining concealed beneath the board’s outer surface.

Diverging from conventional through-hole vias that traverse the entire board thickness, a buried via is strategically positioned within internal layers, optimizing component placement and external layer routing. This strategic configuration contributes to enhanced board performance, minimized signal interference, heightened circuit density, and improved signal quality.

The manufacturing process of a buried via encompasses plating, drilling, and lamination as integral steps during board fabrication. Engineers meticulously plan and implement this via using computer-aided design, considering thermal, electrical, and mechanical parameters. The benefits of a buried via include its compact form factor, reduced electromagnetic interference, and efficient thermal dissipation.

However, a buried via is not without limitations. Its intricate fabrication process can elevate production costs, and the maintenance of its layout presents challenges.

Blind Via

Blind via is a specialized interconnection layout employed in PCB board design to connect the outermost layer with one or more inner layers without traversing the entire board. This facilitates effective signal routing between layers while conserving space on the board. In PCB design, it allocates additional space, making it particularly suitable for HDI PCB and BGA assembly.

Unlike conventional through-hole via, a blind via only penetrates a specific layer. This design aids high-density circuit layouts by connecting traces on the designated layer without affecting others. A blind via enhances overall performance and signal quality by reducing complex layer transitions and signal interference.

The manufacturing process of a blind via involves drilling, plating, and layer buildup. Engineers can use CAD for accurate blind via placement, considering parameters like impedance control, signal timing, and thermal management. This via finds applications in various industries such as telecommunications, consumer electronics, and automotive electronics, where space constraints and signal integrity are crucial.

How to Select PCB Vias

Design Consideration: Begin by evaluating your PCBA project requirements. Assess parameters such as power distribution, signal quality, thermal management, and necessary space. High-speed signal traces may necessitate controlled impedance vias to maintain signal integrity, while proper configuration of ground and power vias is crucial for optimal power distribution and heat dissipation.
Via Size: Size determines its current-carrying capacity and heat dissipation efficiency. A larger via offers lower resistance and improved heat dissipation. A smaller via is favored for densely populated PCB. The balance between size and functionality depends on specific design requirements.
Plating: Copper plating is common for vias to ensure electrical conductivity. Plating affects via performance and reliability. Choose between through-hole copper plating or alternative techniques like ENIG to enhance corrosion resistance.
Aspect Ratio: The aspect ratio, defined as the ratio of via depth to diameter, is significant. A high aspect ratio can lead to uneven plating, drilling challenges, and reduced reliability. Consider your chosen PCB manufacturer’s production capabilities when determining the aspect ratio.
Via and Layer Count: The PCB board’s layer count influences via selection. Multilayer boards often utilize blind and buried vias, optimizing space utilization and signal quality. However, these vias are complex to manufacture and can escalate costs.
Thermal Consideration: Vias play a vital role in thermal management. Strategic placement of vias near heat-generating components dissipates heat and prevents localized overheating. Thermal vias, connecting thermal planes or copper pours, efficiently transfer heat from critical areas.
Manufacturability: Ensure the selected via aligns with the capabilities of your PCB supplier. Some vias may require advanced manufacturing methods, impacting cost and lead time. Effective communication with manufacturers avoids design parameters that hinder the manufacturing process.
Cost Factor: Vias’ complexity and types influence overall PCB manufacturing costs. While a buried and blind via offers design advantages, their manufacturing complexity results in higher costs. Conduct a benefit analysis, comparing advantages with project budget constraints.
Testing and Simulation: Utilize simulation tools to analyze the impact of different vias on thermal performance, signal quality, and overall functionality. Virtual testing identifies issues and optimizes the design before actual manufacturing takes place.

Aspect	Through-hole vias	Microvias	Buried Vias	Blind Vias
Size	0.15 mm to 0.4 mm	0.05 mm to 0.15 mm	0.05 mm to 0.15 mm	0.15 mm to 0.4 mm
Purpose	Interconnect	Interconnect	Interconnect	Interconnect
Layers	All layers	External to inner layers	Inner layers	Adjacent layers
Accessibility	Top-to-bottom	Top-to-bottom	Inside the board	Top-to-bottom or bottom-to-top
Complexity	Lower	Moderate to higher	Higher	Moderate to higher
Manufacturing	Drilling and plating	Laser drilling and plating	Laser drilling and plating	Sequential build-up
Density	Lower	Higher	Higher	Higher
Signal Quality	May have issues	Generally good	Generally good	Generally good
Thermal Management	Moderate	Improved due to the size	Improved due to the location	Improved due to the location
Reliability	Good	Good	Good	Good
Cost	Lower	Moderate to higher	Higher	Moderate to high

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